1. Field of the Invention
The present invention relates to a light emitting device, and more particularly, a light emitting device of a simpler structure capable of ensuring a broad light emitting area and a high light emitting efficiency, while manufactured in a simplified and economically efficient process.
2. Description of the Related Art
In a light emitting device, a material contained therein emits light. For example, a light emitting device may have a semiconductor junction using a diode to convert energy generated by recombination of holes and electrons into light.
A light emitting diode (LED) of a semiconductor junction structure currently manufactured is generally formed by junction of a p-type semiconductor and an n-type semiconductor. In the LED of the semiconductor junction structure, an active layer is disposed between the two semiconductors to emit light tuned to a desired wavelength.
For example, in manufacturing a compound semiconductor LED using at least two elements such as GaAs, typically a heterogeneous substrate is employed to grow the semiconductor epitaxially. Here, crystals grown experience defects due to stress caused by mismatch of lattice constant and thermal expansion coefficient.
Especially, a sapphire substrate, when employed in a nitride semiconductor, results in considerable defects due to a great mismatch between a nitride and the substrate, thereby degrading light emitting characteristics of a light emitting device manufactured.
Also, in the LED of the semiconductor junction structure, the n-type semiconductor and the p-type semiconductor should be grown on one substrate, which is, however, a difficult process.
The LED has been recently fabricated as a nanorod or a nanowire to be utilized as the light emitting device. For example, an n-type nanorod and a p-type nanorod are formed to cross each other in order to emit light at an intersection. Here, the nanoscale device emits blue-shifted light owing to stress induced by decrease in a diameter thereof. Each of the nanorods, even when formed of a material with an identical composition, may have a light emitting wavelength varied by a diameter or a length thereof.
In addition to the LED, efforts have been under way to utilize as a light emitting device a Metal Insulator Semiconductor (MIS) formed of a metal-insulator-semiconductor in use for a conventional capacitor. The MIS device features a simpler structure due to a fewer number of layers required than the aforesaid LED light emitting device, thereby simplifying a manufacturing process and saving manufacturing costs.
FIG. 1A is a cross-sectional view illustrating a conventional light emitting device 10 using an MIS structure. Hereinafter, the light emitting device 10 is assumed to be an m-i-p type light emitting device in which a semiconductor layer 11 is a p-type semiconductor.
The light emitting device 10 includes a semiconductor layer 11, an insulating layer 11 and a metal layer 15, and an electrode 17 formed underneath the semiconductor layer 11. An area A of the semiconductor layer 11 experiences recombination of holes and electrons by tunneling effects of the electrons, thereby generating light.
FIG. 1B illustrates an energy diagram illustrating such a light emitting mechanism. Referring to FIG. 1B, energy levels are plotted in a case where a minus (−) voltage is applied to the metal layer 15 and a plus (+) voltage is applied to the semiconductor layer 11.
With the minus (−) voltage applied to the metal layer 15, electrons e− migrate through the insulating layer 13 by tunneling effects. Subsequently, the electrons e− reach the semiconductor layer 11 and then recombine with holes h+ in a valence band of the semiconductor layer 11 to generate photons.
However, in this MIS light emitting device, light generated when the tunneled electrons e− reach the semiconductor layer 11 to recombine with the holes h+, is lower in light emitting efficiency than other light emitting devices, thus required to be increased in light emitting efficiency.